שלום זכר - מקורות וטעמים

Seif 12 - It is customary to have a meal on the day of the circumcision. Rama: And it is customary to assemble a minyan [i.e., a quorum of ten] for the circumcision meal, and it is considered a “mitzvah meal” [i.e., a meal following the performance of certain commandments]. And anyone who does not participate in a mitzvah meal are like those outcast by God, but only if honest/worthy people are [in attendance] there. But if dishonest/unworthy people are [in attendance at the mitzvah meal], one is not obligated to eat there. It is also customary to make a meal and a feast on the Friday night after the birth of a son, and for people to come and partake [of food] near the baby. This is also a mitzvah meal.